This invention is concerned with surface treated inorganic fillers. More specifically, the invention relates to powdered inorganic fillers containing on their surfaces a combination of carboxylic acids and organosilanes to make the fillers more compatible with thermoplastic resins and to improve properties of thermoplastic compounds made by combining the treated fillers with thermoplastic resins. Filler compositions containing the claimed combination of surface modifiers surprisingly have been found to minimize mold flow lines in injection molded thermoplastic compounds manufactured by blending the compositions with thermoplastic resins.
Surface treated inorganic filler compositions and thermoplastic compounds made with such filler compositions are known in the prior art. However, there is a continuing need to improve the properties of such compositions and compounds and to facilitate their manufacture.
Two prior art patents disclosing alumina hydrate compositions surface modified with carboxylic acids are Bonsignore U.S. Pat. No. 4,283,316 and Levendusky et al U.S. Pat. No. 4,390,653. Surface modification of inorganic fillers with various organosilane compounds is disclosed in Berger U.S. Pat. No. 4,105,465; Smith, Jr. U.S. Pat. No. 4,131,589 and Burhans et al U.S. Pat. No. 4,218,360. None of the patents listed above suggests any combination of carboxylic acid and organosilane surface modifiers for powdered inorganic fillers.
It is a principal object of the present invention to provide a powdered inorganic filler with a surface coating that will cause filled thermoplastic compounds made with the filler to display an improved appearance compared with controls.
A related object of the invention is to provide a surface modified filler composition that exhibits satisfactory processing characteristics and does not impair physical properties when mixed with thermoplastic resins to form filled thermoplastic compounds.
Additional objects and advantages of the present invention will become apparent to persons skilled in the art from the following specification.